(1) The mechanism of 12-0-tetradecanoylphorbol-13-acetate (TPA)-elicited inhibition of EGF binding (TIEB) was investigated. (2) Specific receptors for phorbol esters were obtained in soluble form from mouse brain and their purification and characterization are being pursued. (3) The putative endogenous ligands for phorbol receptors in milk, intestine, pancreas and stomach were found. (4) An enzyme (phorbol-12,13-diester 12-ester hydrolase, PDEH) which specifically cleaves phorbol diester at the 12 position was isolated and characterized. PDEH is not expressed in mouse skin but in present in rat, rabbit, guinea pig and hamster skin. (5) A protein from mouse serum which specifically binds biologically active phorbol diesters was purified and characterized. (6) Endogenous oncopromotine(s) and oncoretardine(s) have been detected in brain. Their purification and characterization are in progress. (7) Isolation and characterization of very potent oncostatin (antitumor promoter) from clams and other mollusks are being carried out.